Pulse and saw tooth wave generators



April 9, 1957 c, CLARKE 2,788,444

PULSE AND SAW TOOTH WAVE GENERATORS Filed Oct. 5, 1954 United States Patent PULSE AND SAW TOOTH WAVE GENERATORS Cliflord' Clarke, Great Baddow, England, assignor to Marconis WirelessTelegraph Company Limited, London, England, a British company Application October 5, 1954, Serial No. 460,394

Claims priority, application Great Britain December 4, 1953 3' Claims. (Cl. 250-27) This invention relates to saw-tooth wave or pulse generators of the kind comprising a thyratron or similar gas filled grid controlled discharge device and a condenser which, when. the device is non-conductive (its normal condition) is charged from the anode source thereof, a pulse or saw tooth wave being generated by removing. or overcoming a blocking voltage (which voltage is identified hereinafter as the first backing-off voltage) normally applied to a control grid of the device so as to cause it to generate a pulse or saw tooth wave by sharply discharging the condenser. The time interval between pulses is at least as great as the charging time of the condenser.

A defect of known generators of this kind is that the discharge device may flash prematurely, before the condenser is fully charged, and thus produce a premature pulse or saw tooth. Such premature flashing is prone to occur due to such extraneous causes as variations in the anode striking voltage, instabilities in the discharge device itself and stray disturbances generally, thereby making the generator erratic in operation, such erraticness being a most serious defect, especially if the output is to be used to actuate controls. The present invention seeks to overcome this defect.

According to this invention there is provided a pulse or saw tooth wave generator of the kind referred to, comprising means for applying to said discharge device a second backing-oil voltage which latter is derived from and dependent upon the charge in the condenser, said second voltage being co-related to said charge on the condenser so as to hold said device backed-oil, whether or not the first backing-oh voltage is overcome or removed, until said condenser is charged to at least a pre-determined voltage.

The invention is illustrated in the accompanying drawing which drawing shows diagrammatically one embodiment thereof. In describing the drawing suitable practical component values will be given in parentheses. These values are, or" course, merely exemplary.

Referring to the drawing, anode potential is supplied from a terminal 1 through a resistance 2 (l megohm) and a resistance 3 (47,000 ohms) to the anode 4 of a first thyratron 5 having a cathode 6, a first grid 7 and a second grid 8. The cathode 6 is earthed and the second grid 8 is returned to earth through a resistance 9 (100,000 ohms). The anode potential suorce preferably consists of super-imposed A. C. and D. C. for example 200 volts D. C. with 200 volts A, C. superimposed. The superimposition of A. C. is to ensure that the thyratron shall not undesirably maintain itself conductive when flashed.

The grid 8 is also connected through relay contacts 10 and a resistance 11 (100,000 ohms) to a suitable negative D. C. voltage of for example 50 volts, the voltage being connected at 12. So long as the contacts 10 are closed, backingpfi voltage is supplied to grid 8 but this voltage is removed if the contacts 10 open.

The anode 4 is connected through a resistance 13 2. (1,000 ohms) to a condenser 14 (1 microfarad) the other side of which is. connected through resistance 15 (220 ohms) toearth.

With the arrangement as so far described, assuming the condenser 14 to be charged, if the contacts 10 are opened to cause. the thyratron to flash over, the condenser 14 will discharge sharply producing a useful pulse which may be taken off from across the resistance 15 and 'fed out in any convenient way for utliz-ation, for example, by means of the resistance capacity output coupling circuits 16 and 17 and the rectifier 18, to the output terminal 19. A saw tooth wave. output may be obtained, if desired, by connecting the output circuit to the other side of the condenser 14 or to the anode 4, i. e. to either end of the resistance 13. A. defect which is experienced is, however, that, if the contacts 10 are opened shortly after a pulse has been generated or a saw tooth wave commenced, and whilst the condenser 14 is still charging, the. time and magnitude of the next pulse or wave are not precisely determined for, owing to possible variations in anode potential, variations in the thyratron, and instabilities and disturbances generally, the thyratron may flash when the condenser 14 reaches a voltage lying within a fairly Wide range.

There is, therefore, provided a potentiometer consisting of the resistances 20 and 21, the resistances being connected between the anode 4 and the terminal 12, and a tap on this potentiometer is connected to the first grid 7. So long as the charge on the condenser 14 is below a predetermined level, the tapped off voltage thus applied to the grid 7 is sufiicient to hold the thryrati'on backed oft, whether or not contacts 10 are open. Until the condenser 14 reaches a predetermined state of charge, opening of the contacts 10 is therefore ineffective to generate a pulse or saw tooth.

The illustrated arrangement also includes means operable at will for preventing the thyratron 5 from producing a pulse or saw tooth. The said means includes a second thyratron 22 which is included in series with the resistances 15 and 13 and also the resistance 3 in a second discharge path across the condenser 14. This second thyratron has its cathode 24 and second grid 23 earthed, and its first grid 25 connected to the terminal 12 through a resistance 26 (l megohm) and a resistance 27 (220,000 ohms). Connected across the resistance 27 is any required number of relays or other contacts 28, which relays or contacts are operable in any required manner (not shown). As will be seen, the closing of any of these contacts 28 completes a circuit to earth from the grid 25 through the resistance 26 and thus removes the backing off bias of the thyratron 22 and causing it to flash over. The flashing over of thyratron 22 discharges the condenser 14 through the second discharge circuit thereby preventing flashing over of the thyratron 5. Due to the inclusion of the resistance 3 in the second discharge circuit, such discharge produces a much smaller pulse across resistance 15 which in this case forms a much smaller part of the total discharge circuit resistance.

While I have described my invention in one of its preferred embodiments, I realize that modifications may be made and I desire that it be understood that no limitations upon my invention are intended other than may be imposed by the scope of the appended claims.

I claim:

1. A pulse or sawtooth wave generator comprising a gas filled grid controlled discharge device, including at least a cathode, a control grid and an anode, an anode voltage source for said device, a condenser connected to said discharge device, means for charging said condenser from said anode voltage source of said discharge device when the discharge device is non-conductive, means to apply a first blocking bias voltage to a control grid of said discharge device, an output circuit connected to said condenser, a charging resistance for said condenser connected between the anode of the discharge device and said anode voltage source, a potentiometer connected across said condenser, a tapping from said potentiometer connected to a control grid of said discharge device for applying thereto a second blocking bias voltage that is deepndent upon the instantaneous voltage across 'said condenser, whereby said discharge device is rendered non-conductive whether or not the first blocking bias volttage is overcome :or removed until said condenser is charged to at least a predetermined voltage.

2. A pulse or sawtooth wave generator as set forth in claim 1 comprising a second discharge circuit coupled to said condenser, said second discharge circuit including a second discharge device to which a blocking bias device is not rendered conductive.

3. A pulse or sawtooth wave generator as set forth in claim 1 comprising a second discharge circuit coupled to said condenser, said second discharge circuit including a second discharge device to which a blocking bias voltage is applied, means for rendering the second discharge device conductive as and when required, a pulse output circuit connected with said second discharge circuit, any pulse produced during the time when the second discharge device is rendered conductive being relatively small as compared with that produced by the flashing of said discharge device when the second discharge device is not rendered conductive, said second discharge device being connected in series with a relatively high resistance, means for normally applying a blocking bias voltage to said second discharge device and means for removing the last mentioned blocking bias voltage so as to cause the second discharge device to discharge said condenser through its associated charging resistance.

References Cited in the file of this patent UNITED STATES PATENTS 2,044,618 Livingston June 16, 1936 2,082,644 Lord June 1, 1937 2,121,117 Conover June 21, 1938 2,197,414 Place Apr. 16, 1940 2,301,195 Brad-ford Nov. 10, 1942 

